Sixth Meeting: 22nd September, 1909.
Dr. Fulton in the chair.
Papers.—1. “The Great Ice Age of New Zealand,” by Professor James Park.
In this paper the author summarised the evidences of glaciation seen in the Wakatipu region, on the east coast of Otago between the Clutha and Waitaki, in Canterbury and Nelson. A detailed description was given of the Taieri moraine, and Kaikorai glacial deposits near Dunedin, and of the boulder-till covering the Hautapu Valley along the Main Trunk Railway in Wellington. He contended that Dr. Marshall was in error in saying that a boulder-clay was relatively thin because formed under the ice. In North America the tills are found 500 ft. thick, and m Germany 670 ft. thick, while a Permo-Carboniferous till found in South Australia is 1,500 ft. thick. Besides, tills are not uniform and continuous sheets, but notoriously irregular. The beautiful, smooth, flowing contours of Otago were the result of ice erosion, as stated by J. T. Thomson in 1875. South America was glaciated for 1,400 miles north of Cape Horn, up to latitude 37o S., and he thought the evidence conclusive that New Zealand had participated in the general glaciation of the Southern Hemisphere. Captain Hutton, in his glacial map of New Zealand, showed nearly half of the South Island covered with a continuous ice-sheet. The author believed there was now sufficient evidence to warrant the belief that the greater portion of the Island was glaciated. He thought the glacial period of New Zealand was due to elevation, which increased the area to continental dimensions, and linked it up with the outlying southern islands, at the same time diminishing the width of sea to the Antarctic. The New Zealand ice-sheet would radiate from the elevated centre of movement towards the sea, and would thus meet the advancing polar ice, which would, however, be kept off the New Zealand shores by the superior thrust of the land-ice.
Mr. G. M. Thomson advanced several reasons from the botanical point of view against the theory that a glacial epoch prevailed in Pleistocene times in New Zealand, and that what now constituted the South Island (which, according to Professor Park, was only separated during that epoch) was then covered with an ice-sheet. (1) The flora of New Zealand contained, according to Cheeseman, 332 genera and 1,415 species of flowering-plants. Of this number 2 genera (Stilbocarpa and Pleurophyllum) and 45 species are peculiar to the Antarctic Islands (Macquarie, Campbell, Auckland, Antipodes Islands, and the Snares); while 26 genera and 452 species are found in the South Island and Stewart Island, but do not range into the North Island. These peculiar South Island forms included such aberrant types as Ranunculus Lyallii, the whipcord Veronicas, the vegetable sheep (Raoulia eximia and mammillaris), the remarkable woolly Haastias, and many other singular plants. They formed one of the most interesting collections to be found in any part of the world. He argued that the extraordinary diversity of form and type which prevailed among these genera and species required a very considerable period of time for its development, and that the differentiation probably dated from an era much antecedent to the Pleistocene. (2) One of the effects of recent glaciation in the Northern Hemisphere was to produce among the woody plants a deciduous type, such plants only, unless specially modified for the purpose, being able to resist the destructive effects of snow. Taking Britain as an example of an area glaciated within recent geological times, he found that of the 1,223 species of flowering plants in its existing flora, only 91 (or 7.4 per cent) were trees or shrubs. Of these, 26 (or 28.5 per cent) were evergreen, but these included all the small-leaved or hard-leaved species, such as Scotch fir, juniper, yew, heaths, gorse, &c., which were not injured by snow. The only soft-leaved evergreen in Britain was the ivy, which did not hurt with snow. All the other trees and shrubs, to the number of 65 (or 71.4 per cent of the whole), were deciduous, losing their leaves on the approach of winter, and so being uninjured by snow. In New Zealand, out of the 1,415 species of flowering-plants 450 (or 31.8 per cent.) were trees or shrubs. Of this number, 398 (or 88.3 per cent) were evergreen, 45 (or 10.1 per cent.) were leafless, while only 2 species of Euchsia were absolutely, and 5 other plants partially, deciduous—that is, at the outside, less than 1.5 per cent. were fitted to withstand the destructive effects of snow. In the face of these facts it is impossible to conceive that this Island had a glacial epoch within recent times. (3.) There exists in New Zealand, and especially in the South Island, what is called a xerophytic or desert flora—a group of plants specially modified to withstand drought. These are principally found on the mountain-slopes and on the plains on the eastern side of the main range of mountains forming the backbone of the South Island. The speaker showed the effects of this range on the moisture-laden winds which strike the
west coast, causing precipitation of their moisture on the west side, and great dryness on the east. He also gave examples of the small amount of moisture which the desert plants lost by evaporation, and stated that, roughly speaking, about 220 species of flowering-plants, found in the inland parts of the Island, belong to this category. He argued that such a flora could not have arisen since the Pleistocene epoch, but that it was probably due to an intensification of the present conditions. An elevation of 5,000 ft. of the central chain of the South Island within comparatively recent times would have been accompanied on its eastern side by an extremely dry climate, tending to the production and survival of a xerophytic flora. It would also serve to account for the glacial phenomena now visible in many parts of the country, for the formation of the great glacier-lakes, and of the West Coast Sounds, with their terminal moraines under the sea outside their entrances. Summing up all the evidence available from a consideration of the existing flora of New Zealand, he pronounced strongly against the possibility of a glacial epoch within recent geological times.
Dr. Benham, treating the question from a biological point of view, said that the question of a Pleistocene ice-sheet covering New Zealand, and continuous with the extension of the polar ice-sheet, was one that had very important bearings on the character of the fauna of these Islands, and any geological evidence there might be which seemed to indicate the existence of such an ice-sheet must be correlated with biological evidence. In the case of the Northern Hemisphere the advance of the ice-sheet forced existing life to migrate to the south, whence it returned on its withdrawal. But here in the south there was no possibility of restocking the land after having been covered by the ice-sheet. The fauna of New Zealand was in many respects of a remarkable character owing to the great specialisation of its members; yet it contained descendants of ancestors which entered New Zealand at various periods from the north, by way of New Guinea and other lands. Thus it was seen that at two periods New Zealand was of much greater extent than at present—indeed, that it formed a small continent, embracing New Caledonia, the Kermadecs, Chatham Islands, and the Antarctic islands, though not necessarily at the same period. In this continental area the descendants of the immigrants became specialised, and since the last period (Pliocene at latest) there had been no communication with any other land. They knew approximately the date of separation of New Zealand from other land-surfaces—in the latter part of the Mesozoic period; when it received many of its invertebrates—probably in the early Pliocene, when it extended so far south as to include the Campbell, Auckland, and Macquarie Islands, and received its southern forms from America, by way of an Antarctic continent. It appeared that Cook Strait was formed in the later Pliocene; hence the fauna of the South Island had ever since that period been isolated from that of the North Island. A mere examination of the differences in the fauna of the two Islands—quite apart from geological evidence—would indicate that the separation had been longer than the Pleistocene, for a considerable period of time was necessary for the evolution of species. Taking as an analogy Britain, which retained its land connection with Europe till after the Ice Age, they saw that in Britain the species were practically all identical with those of Europe; but in New Zealand many of the birds were represented by distinct species in the North and South Islands—as, for instance, the Maori hen, which had one species in the North Island and three in the South Island; Notornis, which had one species in each Island; the moas, which existed down to historic times, had four different species, and even different genera, in the two Islands; and the parrakeet, crow, thrush, robin, tomtit, and weka each had distinct species in each Island. As regarded snails, slugs, and other invertebrates, the same was the case, though they lacked sufficient detailed knowledge to allow of statistics being presented. These differences imply a separation. But if the South Island were covered by an ice-sheet when the northern limit extended to Cook Strait (vide Bulletin, p. 40), all the animals of the South Island must have been wiped out. Whence did the present fauna, then, arrive ? Birds, it will be said, can fly over Cook Strait. True; but there will have been insufficient time for the differentiation of species. But such an explanation is impossible in the case of the snails, worms, spiders, and flightless insects such as the weta: these all required land connection. The earthworms of the South Island could not have been derived from those of the North Island. Perhaps Professor Park would reply that the ice-sheet left part of Marlborough uncovered; but, even if Cook Strait were not as yet in existence, we still lacked sufficient time for the differentiation of species in the two Islands. Moreover, the genera of earthworms were so greatly different that much longer time was necessary. But a still more serious difficulty was incurred when they bore in mind that this Pleistocene ice-sheet “was an extension of the polar ice-sheet” (p. 43). This polar ice-sheet must have covered Campbell and Auckland Islands—as he himself believed to have been the case—for at this time the elevation of the land in the early Pliocene placed these islands in connection with the South Island of New Zealand. This ice-sheet must
have destroyed all animals and all plants in these Islands, and, since they had not been in connection with any land-surface since the Pleistocene, it was impossible for them to have been peopled since that date. Moreover, the species of land-birds on the Auckland Islands were distinct from those of New Zealand. It was not a question merely of their annual flight after the withdrawal of the ice-sheet. That was quite possible, for several introduced birds were observed, but the differentiation of species in these outlying islands was great, and all indicated a long separation; while the presence of the flightless duck, a genus found nowhere else, was even more impressive. As a result of the recent expedition they found, from an examination of the various groups of invertebrates, that, although there were similarities to those in New Zealand, many of them were more nearly allied to South American forms, which could not by any possibility have survived an ice-sheet, or have arrived here after the ice-sheet had withdrawn. It was only possible to explain the occurrence of such existing terrestrial forms, which could neither fly nor swim, which could not survive a sea-bath, by their migration along a land-area extending across the Antarctic region from South America to these Islands. It seemed to him that the onus lay with Professor Park to show how these subantarctic islands became peopled after their fauna and flora had been wiped out by the Pleistocene ice-sheet. The whole biological evidence seemed to be entirely antagonistic to his theory. “Moreover,” he said in conclusion, “I believe that the thesis can be strongly supported that there was no general reduction of temperature over the whole Southern Hemisphere at or about that period.”
Professor Marshall also criticized Professor Park's conclusions adversely, his summary and conclusions being as follows:—A. That an ice-sheet did not reach the east coast of the South Island is proved by—(1.) The absence of moraines near the coast, except at the landward end of the Taieri Gorge, where there have been important earth movements. (2.) The absence of till and boulder-clay. The substances that have been claimed as belonging to this class are—(a) loess in Canterbury and north Otago, (b) residual clays from volcanic rocks at Dunedin, (c) moraine and valley-trains at the Taieri, (d) old sea-beaches at Caversham and at Green Island. (3.) Absence of roches moutonnées. (4.) Absence of striated glacial pavements. (5.) Absence of erratics and of striated boulders. (6.) Absence of a glacial topography in all coastal districts. B. The ice of the Wakatipu glacier. (1.) The occurrence of ice in one valley does not justify the conclusion that the neighbouring valleys were ice-filled. (2.) The thickness of the ice in the ancient Wakatipu glacier appears less impressive when it is realised that the ice in the Tasman Glacier is at the present day over 2,000 ft. thick, and that its base is only 1,600 ft. above sea-level. (3.) If the ice was 7,940 ft. thick at the Hector Mountains and if it had the same surface-slope as the Greenland ice-sheet, it must have extended far over the tops of all the western mountain-peaks, which, however, are not glaciated. (4.) The reversed slope of the Wakatipu basin must have existed during the glaciation. This implies a rapid thinning, which must have been due to melting. Adopting the surface-slope of the Greenland ice-sheet, the terminal face cannot have been east of Lumsden. (5.) The author's estimate of the level of the surface of the ice is 4,000 ft. at Mount Dick. The terminal face would then be at Athol. (6.) There is no ice erosion on the Hokonui Hills, and no moraine or erratics in the Waimea Valley. C. The suggested extension of the Antarctic ice-sheet. (1.) At the present time the ice nowhere extends into deep water. (2.) There was no ice-sheet in Siberia when there was an ice-sheet in central Europe, or in Alaska when the Mississippi Valley was glaciated. (3.) America was not all glaciated simultaneously. (4.) A reduction of temperature in South Victoria Land would cause a decrease of glaciation. (5.) There is an absence of all effects of an ice-sheet at the Campbell and Auckland Islands. (6.) No erratic blocks from South Victoria Land have yet been found in New Zealand. D. The suggested glaciation of the North Island is disproved by the following: (1.) The mapping of the river courses shows no indication of the existence of a glacial topography. (2.) No striated rock-surfaces. (3.) No glacial moraines. (4.) No erratic blocks with striations. (5.) No roches moutonnées. (6.) The “boulder-clays” referred to are deposits laid down by rivers that flowed from active volcanoes during periods of activity. (7.) The deposits at different heights are due to rivers; for as the land was gradually raised the base level of erosion would lie deeper and deeper in the rocks, and portions of the older base levels would be left at various heights. (8.) No valleys with the characteristic form of those due to glacial erosion have yet been described on Ruapehu. (9.) No glacial valleys have been described in other parts of the North Island. In general the writer sees no reason to depart from the view long held by all New Zealand geologists, that the amount of Pleistocene glaciation in New Zealand did not reach to the magnitude of an ice-sheet. On the western side the ancient glaciers reached the coast in many places in the south of the South Island, while on the eastern side they threaded far through the mountain valleys towards the coast.